Transcription factors play a central role in the expression of specific genes upon stimulation by extracellular signals, thereby regulating a complex array of biological processes. Members of the family of transcription factors termed AP-1 (activating protein-1) alter gene expression in response to growth factors, cytokines, tumor promoters, carcinogens and increased expression of certain oncogenes. Growth factors and cytokines exert their function by binding to specific cell surface receptors. Receptor occupancy triggers a signal transduction cascade to the nucleus. In this cascade, transcription factors such as AP-1 execute long term responses to the extracellular factors by modulating gene expression. Such changes in cellular gene expression lead to DNA synthesis, and eventually the formation of differentiated derivatives (Angel and Karin, Biochim. Biophys. Acta, 1991, 1072, 129).
In general terms, AP-1 denotes one member of a family of related heterodimeric transcription factor complexes found in eukaryotic cells or viruses. However, as used herein, "AP-1" specifically refers to the heterodimer formed of c-Fos and c-Jun (Angel and Herrlich, Chapter 1, and Schuermann, Chapter 2 in: The FOS and JUN Families of Proteins, Angel and Herrlich, eds., pp. 3-35, CRC Press, Boca Raton, Fla., 1994; Bohmann et al., Science, 1987, 238, 1386; Angel et al., Nature, 1988, 332, 166). These two proteins are products of the c-fos and c-jun proto-oncogenes, respectively. Repression of expression of either c-fos or c-jun, or of both proto-oncogenes, and the resultant inhibition of the formation of c-Fos and c-Jun proteins, is desirable for the inhibition of cell proliferation, tumor formation and tumor growth.
The phosphorylation of proteins plays a key role in the transduction of extracellular signals into the cell. Mitogen-activated protein (MAP) kinases, enzymes which effect such phosphorylations are targets for the action of growth factors, hormones, and other agents involved in cellular metabolism, proliferation and differentiation (Cobb et al., J. Biol. Chem., 1995, 270, 14843). MAP kinases are themselves activated by phosphorylation catalyzed by, e.g., receptor tyrosine kinases, G protein-coupled receptors, protein kinase C (PKC), and the apparently MAP kinase dedicated kinases MEK1 and MEK2. MAP kinases include, but are not limited to, ERK1, ERK2, two isoforms of ERK3, ERK4 (ERK stands for "extracellular signal-regulated protein kinase), Jun N-terminal kinases/stress-activated protein kinases (JNKs/SAPKs), p38/HOG1, p57 MAP kinases, MKK3 (MAP kinase kinase 3) and MKK4 (MAP kinase kinase 4, also known as SAPK/ERK kinase (SEK) or JNK kinase (JNKK)) (Cobb et al., J. Biol. Chem., 1995, 270, 14843, and references cited therein). In general, MAP kinases are involved in a variety of signal transduction pathways (sometimes overlapping and sometimes parallel) that function to convey extracellular stimuli to protooncogene products to modulate cellular proliferation and/or differentiation.
One of the signal transduction pathways involves the MAP kinases Jun kinase 1 and Jun kinase 2 which are responsible for the phosphorylation of specific sites (Serine 63 and Serine 73) on c-Jun. Phosphorylation of these sites potentiates the ability of AP-1 to activate transcription (Binetruy et al., Nature, 1991, 351, 122; Smeal et al., Nature, 1991, 354, 494). At least one human leukemia oncogene has been shown to enhance Jun N-terminal Kinase (JNK) function (Raitano et al., Proc. Natl. Acad. Sci. (USA), 1995, 92, 11746), thus indirectly demonstrating a role for AP-1 in cellular hyperproliferation and tumorigenesis. Cellular hyperproliferation in an animal can have several outcomes. Hyperproliferating cells might be attacked and killed by the animal's immune system before a tumor can form., Tumors are abnormal growths resulting from the hyperproliferation of cells. Cells that proliferate to excess but stay put form benign tumors, which can typically be removed by local surgery. In contrast, malignant tumors or cancers comprise cells that are capable of undergoing metastasis, i.e., a process by which hyperproliferative cells spread to, and secure themselves within, other parts of the body via the circulatory or lymphatic system (see, generally, Chapter 16 In: Molecular Biology of the Cell, Alberts et al., eds., pp. 891-950, Garland Publishing, Inc., New York, 1983). Using the oligonucleotides of the invention, it has surprisingly been discovered that several genes encoding enzymes required for metastasis are positively regulated by AP-1. Accordingly, inhibition of expression of c-fos and/or c-jun serves as a means to modulate the metastasis of malignant tumors. A method of modulating one or more metastatic events using the oligonucleotides of the invention is thus herein provided.